In genetics, splicing is a modification of genetic information prior to translation.

In eukaryotes, a gene often contains altering sequences known as exons and introns. In contrast to prokaryotes, which do not have introns, the primary mRNA transcript called pre-mRNA (see transcription) from the DNA has to be spliced, that means, the introns are removed from the mRNA in an intramolecular reaction, where the mRNA acts as a ribozyme, with the assistance of spliceosomes. The spliceosome also attaches new noncoding units:

• A 5' cap, a guanine triphosphate nucleotide, thus named because it binds to the 5' end of the mRNA;
• A leader that follows the 5' cap but precedes the exons;
• A trailer that follows the exons;
• A poly-A tail that follows the trailer.

XXXXEEEEIIIEEEEEEEEEEIIIIEEEEEEEEEEXXXX   DNA with exons and introns
           ↓transcription↓
    EEEEIIIEEEEEEEEEEIIIIEEEEEEEEEE       mRNA (primary transcript) with exons and introns
           ↓  splicing   ↓
    CLLLEEEEEEEEEEEEEEEEEEEEEEEETTTTAAAA  mRNA (spliced) with exons, 5' cap, leader, trailer and poly-A tail
           ↓ translation ↓
             polypeptide